Adsorption of copper, cadmium and silver from aqueous solutions onto ...

Adsorption of copper, cadmium and silver from aqueous solutions onto natural carbonaceous materials P. Hanzlík1, J. Jehlička1, Z. Weishauptová2, O. Šebek1 1Faculty

of Science, Charles University in Prague, Czech Republic of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, Prague, Czech Republic 2Institute

ABSTRACT Twelve carbonaceous materials were investigated for adsorption of Cd, Cu and Ag from water solutions. Before the adsorption experiments the chemical and structural characterization of all materials were made. The batch adsorption experiment was used. The kinetic of the adsorption process was very fast for the first five hours but very slow for approximately the next 65 hours. Nevertheless the maximum amount of metal removed was achieved during the first stage of about five hours. Biological materials (milled wood, bark, cork) exhibited a very low affinity for adsorption of metals. The best results were obtained for materials in an intermediate degree of carbonisation with a high content of oxygen rich functional groups. Although the highly carbonised materials exhibited low ability to adsorb copper or cadmium, their capacity to bind silver was very high. Keywords: adsorption; copper; cadmium; silver; wood; peat; coal; activated carbon

A high concentration of cadmium, copper and silver in waters has been identified as a potential health and environmental hazard (Cheremisinoff 1990, Enzminger 1993). The common methods of removal of metals from industrial wastewaters are chemical precipitation, electrolytic extraction, reverse osmosis, evaporative methods, ion exchange and many others (Allen and Brown 1995). The frequent method for decontamination of natural and industrial waters is the adsorption of metals by synthetic ion-exchangers (Enzminger 1993), activated carbons (Newcombe 1994, McKay 1996, Otova et al. 1997), or zeolites (Zamzow and Murphy 1992). Many workers have studied adsorption of soluble metallic species by clays, oxihydroxides or colloids. Khan et al. (1995) studied the adsorption of chromium and silver on bentonite. Fowle and Fein (1999) have studied the adsorption of metals by bacteria. However, these methods are all rather expensive, involving high-priced equipment and energy requirements. Therefore, there is a need for the development of more cost-effective methods. One perspective method is the exploitation of specific natural or industrial waste materials. McKay (1996) reported adsorption properties of activated carbon, peat, lignite or wood. Lignocellulosic materials (kenaf, alfalfa, juniper and aspen) were investigated by Han (1999). Their results show, that these materials are effective as adsorbents of metals (Cd, Cu, Ni, Zn). Removal of copper by ap-

ple residues from a solution was described in the report of Lee and Yang (1997). Numerous experiments carried out over many years have proved the suitability of peat and lignite for the improvement of natural waters (Gosset et al. 1986, Kadlec and Keoleian 1986). McLellan and Rock (1988) reported that adsorption of metals by peat increases with increasing metal concentrations and longer contact time. On the other hand, they recommended using peat for the pre-treatment process only. The primary aim of this research was to determine the adsorption properties of the low-cost natural carbonaceous materials for adsorption of heavy metals from aqueous solutions. The twelve materials used in this study are oxygen-rich adsorbents, humic-rich adsorbents and carbon-rich adsorbents. The goal of this account of our research was to describe the adsorption properties in a continual series of materials, which differ in their degree of coalification, elemental composition, surface oxygen groups content, and structural properties. MATERIAL AND METHODS The studied materials were spruce wood, pine bark, cork, peat from Soběslav in Czech Republic (CZ) and coals of different degree of coalification. Brown coals were represented by fusinite, lignite, leonardite (all from Bílina, CZ). Fusinite is com-

Supported by the Ministry of Education, Youth and Sports of the Czech Republic, Project FRVŠ 1718.

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posed of highly oxidised phytoclasts. Oxidation at Bílina is related to paleofires. Leonardite is highly oxidised form of lignite. Our sample represents paleoweathered coal. Other studied materials were: bituminous coal from Kladno (CZ) and anthracite from Lhotice (CZ). This series was completed with industrial carbon-rich materials: coke, activated carbon Filtrasorb F-400 and MultisorbTM100 (Multisorb TM 100 is the peat-based adsorbent manufactured by PEATEC Corporation, USA). All materials were dried at laboratory temperature, disintegrated and sieved. The fraction size of 1– 2 mm was used for all adsorption experiments and surface properties characterization. Fine fraction under 1 mm was used for elementary analyses. The elementary composition was determined by pyrolysis accompanied with measurements using a CarboErba microanalysator (Borkovcová et al. 1986). The relative amount of oxygen containing surface functional groups was determined by Fourier transform infrared (FTIR) spectroscopy. FTIR spectra were recorded with Nicolet 740 spectrometer using the standard KBr pellet technique (Borkovcová et al. 1986). The relative amount of the carboxylic groups was obtained from the FTIR spectrum by integration of the area in the zone between 1500 and 1800/cm (Yang 1997). The cation exchangeable capacity (CEC) was determined in a leachate of 0.1M BaCl2 (Plume 1990). The mesoand macroporosity were determined by highpressure Hg porosimetry (Mayer and Stowe 1965). This method essentially consists of measuring the extent of mercury penetration into the evacuated solid as a function of applied hydrostatic pressure.

The Porosimeter 2000 was used for this purpose. The surface area was measured by the BrunnauerEmmet-Teller (BET) method (Brunauer et al. 1938) with Sorptomatic 1800 CarloErba apparatus. The BET method is based on the measurement of nitrogen adsorption isotherm at the liquid N2 temperature. Adsorption properties of carbonaceous adsorbents were investigated for interaction with toxic metals Cu, Cd and Ag. Solutions of metals were prepared by the dissolution of CdSO4, CuSO4.5 H2O and AgNO3. Initial concentrations of metals were chosen 50, 100 and 200 mg/l. The starting pH of solutions was equal to 5. The ionic strength of solution is the parameter affecting the adsorption. The ionic strength of solutions (0.1M) was adjusted using KClO4. The kinetic adsorption experiments were made with single component solutions to precede any interactions between metals. Five grams of each adsorbent were shaken with 100 ml of solution for 72 hours. The samples were taken for analysis (Atomic absorption spectrophotometer Varian SpectrAA-200) at regular intervals (0.5, 1, 2, 3, 4, 5, 15, 25, 35, 45, 60 and 72 hours) and pH was measured. The isotherm studies were provided for all materials discussed and the adsorption behaviour was calculated by using the Langmuir equation. RESULTS AND DISCUSSION Textural analysis

The textural properties of adsorbents are presented in Table 1. All investigated materials exhibited

Table 1. Textural properties of the adsorbents Volume of the pores (mm3/g) Material

BET (m2/g)

Vmicro

Vmacro

Vmeso

121

283.7

48.7

Cd was in conformity with order of adsorption for humic acids (Kerndorff and Schnitzer 1980). About presence of humic acids in low carbonified materials we can infer from analysis of the carboxylic groups. Moreover, the order of adsorption capacity of lignite in a single-component system after Allen and Brown (1995) is identical (Cu > Zn > Cd). The majority of other adsorbents exhibit an affinity of adsorption for metals in the order Ag > Cu > Cd. Coke and activated carbon F-400 are characterised by this order: Ag ≥ Cd > Cu. Isotherm calculations

Computer calculations of Langmuir isotherms including adsorption capacities of investigated materials were made. Calculations for spruce wood and pine bark show a low ability to adsorb cadmium and copper. Adsorption isotherms for adsorption PLANT SOIL ENVIRON., 50, 2004 (6): 257–264

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Adsorption capacity (mg/g)

35 Ag

Cu

Cd

30 25 20 15 10 5

coke

anthracite

bituminous coal

fusinite

leonardite

lignite

Multisorb

peat

cork

pine bark

spruce wood

0

Figure 2.Figure Langmuir adsorption capacities of selected materials (mg/kg) 2: Langmuir adsorption capacities of selected materials (in mg/g).

of silver onto wood and bark are of the linear-type. With linear isotherm it is impossible to determine the maximal uptake (adsorption capacity). The highest adsorption capacities of all used metals were calculated for Multisorb (Figure 2). Despite the fact Multisorb is produced from peat, peat displayed a significantly lower capacity than Multisorb for all metals. Nevertheless peat displayed good results for silver and copper. The adsorption capacity for Ag of peat was similar to that of cork (Figure 2). The adsorption capacity of lignite was comparable to peat for Cu. Results for lignite, leonardite and fusinite for Ag were similar. The effectiveness of removing metal ions was the lowest in case of highly carbonified materials (bituminous coal, anthracite). Our results are in agreement with findings of Ong and Swanson (1966), who stated that the adsorption capacity of bituminous coal is much times less than that of the lignite. The adsorption capacity calculations of activated carbon were not done well because of the precipitation of metals in solution. The findings of our laboratory studies are encouraging and should be applicable to potable and industrial wastewaters. Some natural materials (in view of good adsorption properties and low cost) can effectively substitute actually used adsorbents. Acknowledgement

We would like to thank V. Machovič for his study of COOH groups and elementary analysis.


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ABSTRAKT Adsorpce mědi, kadmia a stříbra z vodních roztoků na přírodní uhlíkaté materiály Řada dvanácti uhlíkatých materiálů byla studována z hlediska adsorpce Cd, Cu a Ag z vodních roztoků. Nejdříve bylo charakterizováno chemické složení a strukturní vlastnosti všech materiálů. Pak proběhly vsádkové adsorpční pokusy. V prvních 5 h dochází k rychlé adsorpci kovů, v průběhu dalších ca 65 h je ekvilibrace pomalá. Největší množství kovu bylo adsorbováno během prvních 5 h. Biologické materiály (dřevěné piliny, kůra, korek) vykazují velmi nízkou adsorpci kovů. Nejlepších výsledků bylo dosaženo u materiálů středního stupně prouhelnění s vysokým obsahem kyslíkatých funkčních skupin. Vysoce prouhelněné materiály mají nízkou schopnost adsorbovat Cu a Cd, zatímco jejich schopnost vázat Ag je velmi vysoká. Klíčová slova: adsorpce; měď; kadmium; stříbro; dřevo; rašelina; uhlí; aktivní uhlí

Corresponding author: RNDr. Jan Jehlička, Dr., Ústav geochemie, mineralogie a nerostných zdrojů, Přírodovědecká fakulta, Univerzita Karlova, Albertov 6, 128 43 Praha 2, Česká republika phone: + 420 221 951 503, fax: + 420 221 951 496, e-mail: [email protected]

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